1. Field of the Invention
The present invention relates to an optical information recording and reproducing apparatus for recording information on an optical information recording medium, reproducing the information recorded on the medium and/or erasing the information recorded on the medium. Such an information recording and reproducing apparatus is suitable for use as an information recording and reproducing apparatus which uses a card-like information recording medium on which a plurality of linear information tracks are arranged in parallel.
2. Related Background Art
As a medium for recording information by using light and reading the information thus recorded, disk-shaped, card-shaped and tape-shaped media have been known. Of those, the card-shaped optical information recording medium (hereinafter referred to as an optical card) is compact and light in weight, convenient to carry and has a large memory capacity. Accordingly, a big demand is expected.
On such an optical card, information is recorded as a line of optically detectable record bits (information track) by scanning the card by a light beam which is modulated by recording information and focused into a small spot. In order to exactly record information without trouble such as crossing of information tracks, it is necessary to control (autotracking or AT) an irradiation position of the light beam spot on the optical card in a direction normal to a scan direction. In order to irradiate the light beam as a stable small spot irrespective of curvature of the optical card or mechanical tolerance, it is necessary to control (auto-focusing or AF) the light beam spot in a direction normal to the optical card surface. Further, in order to compensate for any variation in scan speed, it is necessary to obtain a clock signal. In a reproducing operation, the AT and AF are also required.
Accordingly, a tracking track, a clock track or other preformat data is formed on the optical card.
FIG. 1 shows a plan view of a known optical card having a preformat. On an optical card 101, clock tracks 2.sub.1, 2.sub.2, 2.sub.3 . . . having clock signals recorded thereon to form discontinuous broken lines and tracking tracks 31, 32, 33, . . . formed in continuous lines, are alternately arranged at a constant interval. Record areas 4.sub.1, 4.sub.2, 4.sub.3 . . . for recording information are provided one for each of the tracks. The optical card 101 has record areas between the clock tracks and the tracking tracks.
FIG. 2 shows a configuration of an optical card information recording and reproducing apparatus. Numeral 106 denotes a motor for driving an optical card 101 in a direction shown by arrow A, numeral 107 denotes a light source such as a semiconductor laser, numeral 108 denotes a collimator lens, numeral 119 denotes a diffraction grating, numeral 110 denotes an objective lens, numeral 109 denotes a beam splitter, numeral 111 denotes a tracking coil, numeral 112 denotes a focusing coil, numerals 113 and 114 denote condenser lenses, numerals 115 and 116 denote photo-electric conversion elements, numeral 117 denotes a tracking control circuit, and numeral 118 denotes a focusing control circuit. Currents are supplied to the tracking coil 111 and the focusing coil 112 under the control of the control circuits 117 and 118 in accordance with signals detected by the photo-electric conversion elements 115 and 116 so that the objective lens is driven to carry out AT and AF. The photoelectric conversion elements 115 and 116 produce clock signals and reproducing signals. The optical card information recording and reproducing apparatus is constructed by elements other than the optical card 101 and the motor 106 shown in FIG. 2.
A method for recording and reproducing information to and from the optical card by such an apparatus will now be explained.
In the apparatus shown in FIG. 2, a light beam emitted from the light source 107 is collimated by the collimator lens 108 and it is split by the diffraction grating 119 into three beams of different travelling angles with respect to a direction normal to the plane of the drawing. Those beams are reflected by the beam splitter 109 and form three beam spots on the information record plane of the optical card 101 through the objective lens 110.
FIG. 3 shows a partial enlarged plan view of the information record plane of the optical card 101.
When information is to be recorded on the optical card 101, spots S.sub.1, S.sub.2 and S.sub.3 are formed on the information record plane with the spot S.sub.1 being on the clock track 2.sub.1 and the spot S.sub.3 being on the tracking track 3.sub.1. By relatively moving the optical head, which forms the spots, and the optical card, the spots S.sub.1 .about.S.sub.3 are scanned in a direction a. A clock signal is reproduced from a reflection light of the spot S.sub.1. A reflection light of the spot S.sub.3 is directed to the photoelectric conversion element 115 in the optical head, and a tracking signal is produced in the tracking control circuit 117 by a known method such as a push-pull method. The tracking coil 111 is energized in accordance with the tracking signal to horizontally drive the objective lens 110. Thus, the spots S.sub.1, S.sub.2 and S.sub.3 are moved together, normal to the scan direction to perform auto-tracking. Thus, record bits 5 are recorded on the record area 4.sub.1 by the spot S.sub.2 along the tracking track 3.sub.1. When information is to be recorded on the record area 4.sub.2, the spots S.sub.1 ', S.sub.2 ' and S.sub.3 ' are irradiated as shown and a clock signal is reproduced from the clock track 2.sub.2 by the spot S.sub.3 ' and a tracking signal is reproduced from the tracking track 3.sub.1 by the spot S.sub.1 '. Information is recorded by the spot S.sub.2 ' while the autotracking is carried out. In this manner, information can be recorded on all areas of the record area.
FIG. 4 shows a partial enlarged plan view of the information record plane of the optical card 101.
When information recorded on the optical card is to be reproduced, an intensity of the light beam spot to be irradiated to the record bits need not be too high. Therefore, two lines may be simultaneously read. Namely, the spots S.sub.1, S.sub.2 and S.sub.3 are irradiated to the record track 25.sub.1, tracking track 3.sub.1 and record track 25.sub.2. Those spots are scanned in the direction a as was done in the record mode. Since no clocking is required in the reproducing mode, the clock track is not irradiated. A tracking signal is reproduced from the reflection light of the spot S.sub.2 and signals are reproduced from the reflection lights of the spots S.sub.1 and S.sub.3.
In the recording and reproducing of information by the light beam, it is necessary to position the light beam spot to the predetermined tracking track to effect the AT control (AT pull-in of the light beam spot).
In the AT pull-in of the light beam, the optical head is moved to the vicinity of the target track, the light beam spot is formed on the record medium surface, and after a sufficient in-focus state has been attained, the AT servo system is activated to carry out the AT pull-in for the target track.
As shown in FIG. 3, tracks are formed on the optical card or record medium parallel to the scan direction of the light beam spot (direction a shown in FIG. 3).
Accordingly, if the light beam spot is formed in the AT pull-in mode at an intermediate point between the tracks on the record medium, the AT pull-in is not attained.
In the prior art optical card recording and reproducing apparatus, the entire optical head is moved orthogonally to the tracks of the optical card (direction b in FIG. 6) and when the tracking light beam spot reaches the position corresponding to the desired tracking track, the AT control is started so that the AT pull-in is attained for the target track.
However, when the optical head is to be moved to cause the light beam spot to move across the tracks, the actuator is rapidly driven and the light beam spot moves beyond the desired tracking track and the AT pullin is not attained for the target track. In order to attain exact AT pull-in in this method, it is necessary to slow down the drive speed of the optical head and hence, a long time is required to attain the AT pull-in.
As shown in FIG. 7, it has been proposed to scan the tracking light beam spot slightly obliquely (direction c) with respect to the direction of the tracking track 3.sub.2 so that the light beam spot crosses the tracking track and the AT pull-in is carried out during the period.
However, this method requires a relatively long distance scan and hence requires a long time to attain the AT pull-in.